the contents into your PES 2019 installation directory (specifically inside the sider folder).

of the stadium pack (Part 1, Part 2, etc.) to the same folder.

Inside the RAR file, you will usually find a content folder, which should be moved to your Sider installation folder. Typical Installation Steps

to ensure the stadium-server.lua module is enabled.

only "part1". The software will automatically combine the parts.